1. Field of the Invention
The present invention relates to a hollow golf club head, and particularly to a golf club head being of a wood type or similar type thereto.
2. Description of the Related Art
As wood-type golf club heads such as drivers and fairway woods, metallic heads of a hollow shell structure are widely in use. Generally, the hollow wood-type golf club head has a face portion for hitting a ball, a crown portion constituting an upper surface portion of the golf club head, a sole portion constituting a bottom surface portion of the golf club head, a side portion constituting side surface portions on the toe side, the rear side, and the heel side of the golf club head, and a hosel portion. A shaft is inserted into the hosel portion, and is fixed by an adhesive agent or the like. It should be noted that golf clubs called utility clubs are also commercially available on the market in large numbers, and various golf clubs having a head similar to the aforementioned wood-type golf club head (i.e., having the face portion, the sole portion, the side portion, the crown portion, and the hosel portion) are also commercially available on the market.
As metals for forming this hollow golf club head, an aluminum alloy, stainless steel, and a titanium alloy are used. The titanium alloy, in particular, has come to be used widely in recent years.
Generally, it becomes possible to enlarge the sweet spot by increasing the volume of the hollow golf club head. If the volume is increased, the weight of the golf club head tends to increase correspondingly. Accordingly, to prevent an increase in the weight, it has been conceived to adopt a fiber reinforced resin whose specific gravity is smaller than those metals.
JP-A-2001-340499 discloses a golf club head in which a face portion and a sole portion are made of a metal, and the other portions including a crown portion and side portions on the toe side and the heel side are formed of a carbon-fiber reinforced thermosetting resin (CFRP ). If the crown portion is made of CFRP, the flexure of the crown portion becomes large during ball hitting, so that it is possible to make the launch angle large, and increase the coefficient of restitution. With this golf club head, however, the seam between a peripheral edge of the face portion, on the one hand, and the crown portion and the side portion formed of CFRP, on the other hand, is in an abutted state. During ball hitting an extremely large stress occurs in this seam between the peripheral edge of the face portion and the crown portion and the side portion. If the golf club head is used repeatedly, this joint portion is likely to peel off.
JP-A-2003-62130 discloses a golf club head in which a front edge portion of the crown, a front edge portion of the sole, and both side front edge portions are forged of titanium integrally with the face portion to be a face element, a body formed of a resin material is joined to this titanium-made face element continuously therewith, and an aluminum plate is disposed on the sole portion. Since this face element includes the front edge portion of the crown, the front edge portion of the sole, and the both side front edge portions, it may be possible that the bonding strength between the face element and the resin-made body can be made greater than that of the seam between the CFRP-made crown portion and the metallic face portion in JP-A-2001-340499 mentioned above. It should be noted that in the golf club head of that publication, an aluminum plate at the sole portion is superposed on the titanium-made face element from below.